Italy to Greece and Back

Hello.

I will be going to Greece from Italy at the end of September. I want to start in Athens and then go to the islands...likely Santorini, Paros, Naxos, Ios.

Questions:

1. Best place to leave from Italy...I'm thinking Venice?
2. Fly or ferry from Italy to Athens? approximate cost differences?
3. Recommended ferry lines from Athens to these islands? Ferry v. hydrofoil?
4. I have to be back in Rome after Greece...so suggestion on order of the islands and is ferry only way back to Athens from the islands or are there local flights (from the islands to Athens...or Rome for that matter)?

Jen